Yes, it's not a panacea. But it's a heck of a lot easier to store a generic supply of printer feedstock, than to store one (or more) of every part that might conceivably break.

Suppose that you expect 1% of all replaceable parts to break over some projected lifespan. Then the mass of feedstock required would be 1% of the mass of the replacement parts... and would take up less than 1% of the space.